Physics, asked by ashima14, 1 year ago

please please answer this question I will mark you as their brain list explain how

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Answered by knavdeep1702

hey mate,

the focal length is 10 cm.

since the image distance is equal to the object's distance from the lens which is only possible when the object is placed at 2F.

and focal length=half of 2F..

hope this helps

Victor36: i got it 20 cm by lens formula

knavdeep1702: u took u positive??

arohisachar14: its convex so u becomes negative

knavdeep1702: yes

knavdeep1702: but in both the lenses u remains negative

arohisachar14: yes but in convex v and f is positive right so by using lens formula you'll add 1/20 and 1/20 instead of subtracting

knavdeep1702: u are right but u see na u=v

knavdeep1702: this is only possible when the object is placed on 2f

arohisachar14: the answer is 10 only no matter how yoi get it so we both are right :)

knavdeep1702: yeah

Answered by arohisachar14

since it is a convex lens,

u is negative

v is positive

and f is positive aswell

now applying 1/f = 1/v-1/u

1/f = 1/20 - 1/-20

so 1/f = 1/20 + 1/20

2/20 +i/f

therefore f = 10cm-option b

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